Silencers are used in air distribution HVAC systems, ventilation systems and other air movement systems for either air and gas streams. Silencers typically employ rectangular sound absorbing elements such as baffles (otherwise known as splitters), in either a round or rectangular cross-sectional duct or support structure, such as a round or rectangular shaped casing. Silencers may include one baffle or several parallel baffles along the width of the duct or casing. The baffle may be uniform along the length, such as a rectangular silencer, or may be transitional where the inlet cross-section is not equal to the outlet cross-section.
Silencer attenuation may be described as either a transmission loss (TL; dB) or an insertion loss (IL, dB). TL is a measure of the sound power upstream versus the sound power downstream from the silencer air opening(s). IL is a measure of the change in the sound level at a defined point of reception (e.g., outdoors, within a room, etc.) with and without the silencer installed.
For a sound absorbing silencer, the attenuation is primarily achieved using acoustic media fill that provides a dissipation of the sound energy as it travels through the silencer's baffle assembly. The acoustic media fill may include, but not be limited to, fiberglass fiber, rock wool or natural cotton media. The acoustic media is typically protected using a perforated metal liner that is integral to the casing surrounding the acoustic media. The combination of the acoustic media fill and the perforated casing typically encompass the complete baffle assembly, and represents the absorptive silencer state of art.
In order to achieve higher levels of sound attenuation within the low frequency range, baffle lengths tend to increase significantly primarily due to the relatively larger wavelengths of the sound. Silencers with rectangular shaped baffles introduce aerodynamic losses due to the nature of the silencer orientation and installation conditions, resulting in blockage of the cross-sectional area, and aerodynamic friction and dump losses. The net aerodynamic losses are quantified as a total pressure drop or pressure resistance. Lower aerodynamic losses are desirable for most systems, as lower energy would be required to move a given volume or mass of air.
Although it is desirable to achieve higher levels of sound attenuation, simply improving sound attenuation by increasing the length of the baffles is undesirable due to i) the increased friction and aerodynamic losses, ii) added space and installation requirements, as well as iii) additional costs related to manufacturing, handling and installation of larger baffles.
The present invention seeks to improve upon the construction design and installation of baffle type silencers in a unique fashion to improve the attenuation of the silencer.